Especially in exploring for disposal sites for nuclear waste, it is necessary to know what kinds of flows are found in the bedrock and in different fractures thereof. In other words, what the direction and velocity of these flows are.
In these kinds of measurements, problems are being posed by small flow rates and velocities. In prior art, flow rates have been tried to be determined by separating a section from a hole drilled in the bedrock, and by filling it with a suitable mixture or solution, so that flows can be measured by observing the concentration changes of this mixture or solution. However, this method does not provide any information on the direction of the flows.
The flow directions have been tried to be determined by means of different tracers, the passage of which in bedrock fractures can be observed.
The problem with all known flow measuring methods is their slow functioning. Because the order of the flow rates is about one milliliter per hour, it takes typically months to perform one measurement, and obtaining information from a wide area and from a number of boreholes is therefore costly and slow.
The above-described problems have been alleviated by means of the flow meter in accordance with Finnish patent FI110335, in which ring-shaped sealing members are used to separate from a hole a specific section of volume, which is then divided by means of dividing members, expandable by internal pressure, into sectors, and the flows between the sectors are measured in flow channels which connect them together. The device is well-functioning and extremely accurate, but has a complex structure and is therefore costly and relatively slow when used in deep holes.
Another flow meter descriptive of the prior art has been disclosed in Finnish patent FI110336. It is based on separating, by means of discoidal separating members, a section to be examined from the measure hole, and connecting this measure section with the exterior thereof via a measure channel, so that information can be obtained of flows passing into the separated section from fractures in the bedrock and back into them. The device is thereby used for measuring the flow passing from the bedrock into the hole or from the hole into the bedrock. It is appropriate for the function it was developed for, but it cannot be used to measure the exact directions and rates of flows which are transverse to the hole, i.e. flows which intersect the hole.